Inspection of welds in components for developing defects, including cracks, is an important and necessary safety procedure. Components operating while experiencing loads can develop defects over time, such as those associated with cyclical fatigue or degradation from wear. Determining the presence and extent of such defects allows an opportunity to repair or replace components.
Defects that can develop under operating conditions can sometimes be difficult to locate during unloaded conditions. For example, a component undergoing strain during operation experiences the operating loads in a deformed shape, as opposed to an unloaded, undeformed shape. When the deformed shape develops defects, they may not be readily observable in the undeformed shape.
One example of difficulty in locating defects occurs in welds. Certain welds, when operating, can develop cracks while bending under strain. After the operating load is removed, the release of strain through unbending can close the cracks, making detection difficult, even with penetrating inspection techniques, such as Fluorescent Penetrant Inspection (FPI).